The present invention relates to machine controls and, more particularly, to a switch assembly for activating a machine.
Many types of automatic machinery such as hydraulic presses, injection molding machines, milling machines, grinders, and the like require the machine operator to place his or her hands between moving parts or within pinch points of a machine during each machine operating cycle to load and unload work pieces from the machine. It is therefore important for the safety of the machine operator that the machine be rendered incapable of actuation until the machine operators limbs, particularly, the operators hands and fingers are safely removed from between these moving parts. To ensure operator safety, it is well known in the art to use a widely spaced pair of switches which do not require exertive contact to initiate a machine cycle. The switches are spaced apart so a machine operator is forced to utilize both hands to activate the machine, thus, decreasing the possibility of the operator's hands being caught within the machine. It is also known in the art to use switches which are non-contact and non-exertive such as photo-optic switches to prevent repetitive motion injuries to the machine operator. U.S. Pat. Nos. 4,939,358 to Herman et al and 5,168,173 to Windsor are typical photo-optic machine controls which require that an operator utilize two hands to operate a machine.
However, several common problems exist with prior art photo-optic machine controls. Most controls have hand sensors which open skyward and are positioned to receive hands entering from above the sensor. In these, the upward facing sensor is susceptible to fouling from airborne dirt and dust and can be triggered accidently by objects falling into the sensors.
Additionally, the American National Safety Institute (ANSI) requires that top mounted dual sensors on machine controllers be separated by at least 22 inches to preclude a person with large hands from triggering both sensors with one hand. This requirement has resulted in machine controllers which are greater than 22 inches long. Controllers greater than 22 inches long are not conveniently usable in operator positions where space is limited. In addition, the wide spacing of top mounted sensors can cause shoulder fatigue by diminutive controller users who must hold their arms spread wide apart when using the controllers. ANSI does permit end mounted sensors to be separated by only 10 inches but controllers having end mounted sensors are not common in the art.
Thus, a need exists for a solid state machine control which has sensors that are shielded from fouling by dirt and airborne dust, which are not susceptible to accidental machine actuation, and which are mounted such that the overall length of the machine control is less than 22 inches in length for use where space is limited and to reduce user shoulder fatigue.